Glutathione-S-transferase, purified from human liver and rat liver, shows multiple catalytic activities and also functions as a bilirubin transport protein. The relationships between the catalytic and ligand binding properties are under study. Particular emphasis will be placed upon evaluating the role of glutathione in the multiple functions. Fluorescence binding studies, kinetic analysis and circular dichroism studies are in progress. The glyoxalase system, including glyoxalases I and II, has been purified from rat erythrocytes. The role of the zinc ion in glyoxalase I is being evaluated using a variety of metal ions in place of the zinc ion. Glyoxalase II is being evaluated as a model thiolesterase.